Anatomical connectivity and a possible behavioral advantage of visual cortex transplants will be assayed. The goal is to determine the possible therapeutic advantage of replacing damaged sensory tissue with neural transplants. The transplants will be posterior cortex tissue taken from embryonic rats; the tissue will be transplanted into the visual cortex of neonatal and adult rats that have received a large visual cortex lesion. After four months, transplant connectivity will be assayed using standard retrograde and anterograde tracing techniques. Possible direct pathways for visual information to reach the transplant will be assayed autoradiographically following transneuronal transport of tritiated amino acids from the eye. More indirect pathways will be examined by determining sites that both receive retinal input and project to the transplant. The retinal projections will be mapped with autoradiographic techniques, and also with degeneration methods following eye removal; neurons which project to the transplant will be determined by mapping horseradish-peroxidase (HRP)-positive cell bodies after injection of the enzyme into the transplant. A possible functional advantage of the transplant will be assayed by testing these animals' ability to discriminate two complex visual patterns, using a task known to be moderately difficult for normal rats, and on which our animals with lesions but no transplant are likely to be seriously deficient. Both the behavioral and anatomical assays will be conducted with rats that received transplants at one of several stages of their visual system development. This study will thus examine host age differences in the anatomical connections and functional contribution of these neural transplants.